Bare opaque ids without a digit are rejected, and bad ids surface as raw SDK errors

Two small things I ran into while working on #64, both reproduced on 3.4.0 (aa8e93a). Neither is a regression from that PR.

Bare opaque ids are rejected when they contain no digit

tdc conversation done CDMDzXhBNCgyQZjkDnqwG --dry-run
# Error: INVALID_REF
# Invalid conversation reference: CDMDzXhBNCgyQZjkDnqwG. Use an id, id:<id>, or a Comms URL.

tdc conversation done id:CDMDzXhBNCgyQZjkDnqwG --dry-run
# [dry-run] Would archive conversation: ...

Expected: the bare form works, like tdc thread view Cf9TR6CPC2dKQL5fB2EoL does.

It's not conversation-specific; the three resolvers in refs.ts are identical. parseRef only treats a bare token as an id when looksLikeRawId passes (refs.ts:68, 151), and that requires at least one digit. The fallback looksLikeOpaqueCommsId (refs.ts:75) only accepts a Cb prefix. This id has no digit and starts with CD, so it's parsed as a name. Swap any letter for a digit, or the prefix for Cb, and the same command reaches the API. Base58 has 9 digits in 58 characters, so a 21-character id comes out digit-free about 3% of the time ((49/58)^21), roughly one id in thirty.

A malformed or missing id surfaces as a raw SDK error

tdc thread view id:nope
# CommsRequestError: Request failed with status 409
#     at fetchWithRetry (.../comms-sdk/dist/esm/transport/fetch-with-retry.js:28:23)
#     ...

tdc thread view Cf9TR6CPC2dKQL5fB2EoL --comment id:nope     # same
tdc thread view id:nope --json
# {"error":{"code":"INTERNAL_ERROR","message":"Request failed with status 409"}}

Expected: a CliError (NOT_FOUND or INVALID_REF) with a hint, per AGENTS.md.

The 409 is the API's "id must decode to 16 bytes" (error_code 217); a well-formed id that doesn't exist gets a 404 and prints the same stack trace. The catch in api.ts maps 403 (both flavours) and 401 and rethrows everything else (api.ts:192-220), so 404 and 409 fall through to the generic branch in index.ts:230.

Happy to open a PR for either if useful.

Start with the three resolvers and parseRef in src/lib/refs.ts, then inspect the error mapping in src/lib/api.ts and the generic branch in src/index.ts, reproducing the listed commands. Done means digit-free bare opaque IDs resolve like explicit ids, while missing or malformed IDs produce the expected hinted CliError instead of a raw SDK error.